This invention relates to fabric softening compositions for use in laundering operations. More particularly, this invention relates to improved fabric softening compositions containing a smectite-type clay and a quaternary ammonium compound which provide improved softening effects.
The use of clays in combination with quaternary ammonium compounds (also referred to herein as "QA" compounds for convenience) is extensively described in the prior art. U.S. Pat. No. 3,886,075, for example, describes a composition containing a smectite clay, a water-insoluble QA compound and an "amino compatibilizing agent" which is said to provide fabric softening and anti-static effects. U.S. Published Patent Application No. B 305,417 describes a granular laundering composition comprising a soap-based granule, a smectite-type clay and a quaternary ammonium anti-static agent. In U.S. Pat. No. 3,862,058, a clay and a quaternary ammonium compound are added to a non-soap synthetic detergent compound to provide a granular laundry detergent composition. U.S. Pat. Nos. 3,993,573 and 3,954,632 describe fabric softening compositions containing the aforementioned clay and QA compounds in combination with a so-called "acid compatibilizing agent". U.S. Pat. No. 4,292,035 discloses a softening composition comprising smectite clay; an amine or quaternary ammonium compound as a softening agent; and an anionic surfactant wherein the fabric softening agent is reacted with the clay to form an "organo-clay complex" prior to the addition of the anionic surfactant.
A common drawback of the aforementioned softening compositions of the prior art is that they require unduly high concentrations of QA compounds to achieve the desired softening effect. Thus, for example, in the detergent compositions described in the examples of U.S. Pat. Nos. 3,862,058; 3,954,632 and 3,993,573, the weight ratio of clay to QA compound is about 5:1. In U.S. Pat. No. 3,948,790 and Published Application No. B 305,471, the examples describe detergent compositions containing 5%, by weight, of QA compound. The use of such relatively high concentrations of QA compound in the aforementioned compositions of the prior art has two distinct drawbacks: first, since QA compounds are relatively expensive softening agents compared to clay, it is economically desirable to provide the desired softening properties using a minimum amount of QA compound relative to the clay in the laundry composition; and second, the QA compounds being cationic are capable of reacting with anionic detergents and brighteners present in detergent compositions, such reactions being preferably avoided insofar as they may inactivate the fabric softener or adversely affect the laundering capability of the composition. Consequently, there is a need in the art for fabric softening compositions containing minimized amounts of QA compounds but still capable of providing the desired degree of fabric softening.
Achieving the aforementioned objective is particularly desirable for laundering compositions intended for use in a soak plus hand-wash operation as compared to laundry operations in a washing machine. In the latter operation, clay is inherently more effective as a softening agent insofar as it comes into contact with and is deposited upon the surface of the fabric being laundered during the wash cycle of the machine when the washing bath is mechanically drained through the fabric. However, in a hand-wash procedure where the mechanical action is not sufficient to effect a similar degree of contact between the fabric and the clay, significantly larger amounts of clay and QA compound must be employed to achieve comparable softening of the fabrics being laundered.
The methods described in the art for preparing the aforementioned fabric softening compositions are varied. However, a common characteristic of such processes is their difficulty in being able to produce a composition capable of providing the desired degree of fabric softening using minimized amounts of clay and QA compound. The preparation techniques of the prior art are thus characterized by either a deposition of QA compound upon granules composed of a uniform blend of clay with detergent and other ingredients (rather than a preferential deposition upon clay granules) or alternatively, the QA compound is reacted with the clay to provide a modified clay in which preferably from about 10 to about 60 mole percent of the exchangeable cations are alkyl substituted ammonium ions. Thus, for example, U.S. Pat. Nos. 3,862,058 and 3,886,075 describe a method of preparation whereby the clay is initially admixed in a crutcher with the detergent, builder and other ingredients of the laundering composition and the resulting mixture then spray-dried to form granules. The QA compound is thereafter sprayed upon the granules from a melt, it being a critical aspect of the method of preparation to avoid spraying the detergent granules with an aqueous solution or suspension of the QA compound. U.S. Published Patent Application No. B 305,417 discloses a method of preparation wherein clay is mixed with soap-based granules in a drum mixer. The QA compound is then added to the resulting composition by spraying from a melt. U.S. Pat. No. 3,594,212 describes a method of softening fibrous materials wherein such materials are successively impregnated with an aqueous dispersion of clay and an aqueous solution of QA compound, the amount of QA compound in solution being sufficient to effect at least a partial cation exchange with the clay retained on the fibrous material. In U.S. Pat. No. 3,948,790 to Speakman, there is described a procedure for preparing "quaternary ammonium clays" whereby a QA compound is reacted with clay by slurrying the untreated clay in a solution containing the desired quantity of QA compound. The QA compounds which may be thus employed are said to be restricted to short-chain compounds having a maximum of four carbon atoms per chain, the total number of carbon atoms in the compound not exceeding eight. The quantity of such QA compound added to the solution is controlled so as to provide the desired degree of ion exchange with the clay. The examples of the patent describe various treated clays in which from about 5 to 40% of the exchangeable cations are replaced by quaternary ammonium cations, the amount of QA compound in solution being necessarily restricted to that which is required to effect a partial exchange reaction with the clay. Accordingly, the prior art does not contemplate the formation of a surface modified clay as herein described.